Delay line structure for traveling wave devices

ABSTRACT

An RF wave periodic delay line is disclosed having thermal energy dissipation and support structure of an insulating material with reduced &#39;&#39;&#39;&#39;dielectric loading&#39;&#39;&#39;&#39; between adjacent elements. For devices requiring internal attenuation to prevent undesired oscillations the appropriate attenuator structure is mounted independently of the dissipation and support structure.

[4 1 June 13, 1972 3,397,339 8/1968Beavereta1..,.........................3l5/3.5

[54] DELAY LINE STRUCTURE FOR 3,387,168 Beaver et al.

TRAVELING WAVE DEVICES 5 33 55 ll. 3 m n m mm SF. 91 67 99 H 00 ll 38 49so 71 33 [72] Inventor: Robert McCowan Unger, Wayland,

[73] Assignee: Raytheon Company, Lexington, Mass. 3,610,999 10/1971Falce......................................3l5/3.5

[22] Filed: Feb. 25, 1971 Primary Examiner-Herman Karl SallbachAssistant Examiner-Saxfield Chatmon, Jr.

Attorney-Harold A. Murphy, Joseph D. Pannone and Edgar 0. Rest [21]Appl. No.:

[52] U.S. Cl. ....3l5/3.5, 333/31 A, 29/600,

[57] ABSTRACT An RF wave periodic delay line is disclosed having thermal[58] Field ofSearch.....................

energy dissipation and support structure of an insulating material withreduced dielectric loading between adjacent elements. For devicesrequiring internal attenuation to prevent undesired oscillations theappropriate attenuator References Cited structure is mountedindependently of the dissipation and support structure.

UNITED STATES PATENTS 3,387,170 6/1968 Farney et a1. 5 3,505,730 4/1970Nelson.....................................29/600 3,345,533 10/1967Washburn, Jr............ 315/3 6 RF IN HELIX DELA Y -L/NE 20 minimum[912 3,670,197

swan 10F 2 RF IN 4-+ HEL/X DELAY/ LINE 20 F/G 2 F/G. 3

PATENTEDJUH 13 I972 3.670.197

sum ear 2 DELAY LINE STRUCTURE FOR TRAVELING WAVE DEVICES BACKGROUND OFTHE INVENTION 1. Field of the Invention The invention relates to slowwave propagating delay structures for traveling wave devices.

2. Description of the Prior Art Traveling wave devices conventionallyutilize continuous wave propagating structures comprising a plurality ofperiodic circuit elements. Such structures reduce the velocity of RFelectromagnetic circuit waves and permit interaction with an electronbeam to result in growing waves with a net exchange of energy. Asynchronous relationship between the relative velocities of the electronbeam and a space harmonic of the traveling waves results in theestablishment of the interaction phenomenon.

An example of such devices is the O-type which incorporates a periodicdelay line structure with an electron beam traversing its axial length.These devices operate on the principle of the exchange of kinetic energyof the electrons with the RF circuit fields. The combined fields induceperturbations in the electron beam and form alternating energy electronpackets which amplify RF energy on the delay line structure. The helixis a commonly employed structure in traveling wave amplifiers comprisinga plurality of continuously wound circuit elements of a tape orconductive wire in a unifilar or bifilar arrangement supported byinsulators. The helix is preferred due to, its broad bandwidthcapabilities and high gain per unit length. At high RF power levels thehelix becomes excessively heated by electron beam interception and RFlosses. The supports, therefore, should dissipate the intense thermalenergy.

Another factor to be considered in the utilization of a helix structureis the requirement for the attenuation of oscillations due to excessivehelix length or reflections of energyat the input and output transitionsfrom the delay line to transmission lines. Lossy material is, therefore,provided in a selected axial region of the delay line by a coating of,for example, carline bon or graphite on delay line supports such asparallel elongated ceramic or glass rods.

The principal difficulty in the design of efficient delay linestructures in the prior art has resulted from the requirement for RFisolation and thermal energy dissipation coupled with the need forsuppression of undesired oscillations. The art is replete withreferences to the utilization of supports of dielectric material such assapphire rods extending along the longitudinal axis of a helix delayline structure. The net effect of sucha structure is that the dielectricmaterial is disposed between the circuit elements where the electricfields of the.

SUMMARY OF THE INVENTION In accordance with the teachings of theinvention, a delay line structure is supported by insulator and thermaldissipation means contacting each of the circuit elements. Theconfiguration of the support means is selected to avoid high electricfields of the RF wave associated with the circuit. In an illustrativeembodiment, an arch-shaped notch is provided in the interval between thecircuit elements to form an undulating wall configuration. The high gaintraveling wave amplifiers are provided with internal attenuation means,which may be of the bulk or surface type, separately and independentlyof the support and thermal dissipation means. Strips or vanes of a lossymaterial, in any desired shape to provide both axial and radialadjustment, are disposed on the perimeter of the delay line structureand span a plurality of desired periodic circuit elements. Inalternative embodiments the configuration of the attenuator material maybe patterned to introduce such material in the interstices between thecircuit elements with a max imum concentration of such material disposedin only a few elements and then being gradually reducedover a portion ofthe axial dimension.

A wide range of selection of materials, as well as the overall quantityutilized, is now available in traveling wave devices by reason of theseparation of the support and attenuation functions. The invention canbe utilized in different delay line configurations such as the ring andbar arrangement in addition to the helix type. The bulk attenuatorprovided by the structure of the invention represents a markedimprovement over the surface type attenuation heretofore utilized inprior art structures. In addition, a mechanically simplified delay linestructure is provided with improved electrical characteristics by theelimination of lossy coatings on support structures.

BRIEF DESCRIPTION OF THE DRAWINGS The invention, as well as the detailsfor the provision of a preferred embodiment, will be readily understoodafter consideration of the following detailed description and referenceto the accompanying drawings, wherein:

FIG. 1 is a detailed cross-sectional view of a traveling wave deviceembodiment utilizing the delay line structure of the present invention;

FIG. 2 is an enlarged detailed cross-sectional view of a portion of theinsulator support and thermal energy dissipation structure of the delayline in FIG. 1;

FIG. 3 is an enlarged cross-sectional view of a portion of theattenuator structure associated with the delay line in FIG. 1;

FIG. 4 is a detailed cross-sectional view of the embodiment of theinvention taken along the line 44 in FIG. 1;

FIG. 5 is a detailed cross-sectional view of an alternative embodimentof the present invention; and

FIG. 6 is a detailed cross-sectional view of a portion of an alternativeattenuator structure.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 thetraveling wave device 2 incorporating the embodiment of the inventioncomprises a conductive envelope 4having mounted at one end an electrongun assembly 6 including, in the order named, a cathode 8, focusingelectrode 10 and accelerating electrode 12. Appropriate voltages areapplied by means of leads 14 for operation of the device and theelectron gun assembly. A collector electrode 16 is provided at theopposing end of the envelope 4 to intercept and dissipate the electronsin the beam traversing the path defined along the longitudinal axis ofhelix delay line structure 20 which is illustrated as being of theunifilar configuration.

A magnetic field is produced by electromagnetic means 22, such as asolenoid, to assist in the orientation of the electron beam within thedelay line structure 20. In the traveling wave amplifier illustrated,the electron beam has a phase and group velocity and the RF energypropagating along the helix delay line structure has a circuit phase andgroup velocity characteristic. With the proper synchronism condition,beam energy is transferred to the circuit. The electron beam and the RFwaves are illustrated as traveling in the same direction. Since there iscoupling of only the waves traveling in the forward direction, thedevice is referred to as a forward traveling wave amplifier. The RFenergy is coupled into the delay line 20 by means of an input coaxialline 24. The amplified energy is coupled from the delay line structureadjacent to the collector end of the envelope by means of output coaxialline 26. If the electron beam is synchronized with backward spaceharmonic waves, the positioning of the input and output coaxial couplinglines is reversed. Numerous systems for the circulation of fluidcoolants in or around the elements of the delay line structure have beendisclosed in the art and need not be further described herein to assistin an understanding of the invention.

Delay line structure defines a plurality of continuously wound periodicelements 28, of a tape or conductive wire to evolve the conventionalhelix sheath structure employed in traveling wave devices. The delayline structure 20 is supported by a pair of insulator members 30, of adielectric material in contiguous relationship with each of the periodiccircuit elements 28 and envelope 4. Referring now to FIGS. 2 and 4, thesupport members 30 are provided with a plurality of arch-shaped notches32 in the regions defined between circuit elements 28. The removal ofthe support material in what may be referred to as the perturbingregion, follows an undulating pattern closely analogous to the RFelectric field provided between the circuit elements. Exemplarydielectric insulating materials having the desired properties forsupport members 30 include beryllia, alumina or boron nitride. Theremoval of the dielectric material from the region spanning all thecircuit elements by means of the notches 32 reduces the dielectricloading" phenomenon. An insulator support structure is thus providedwhich is principally outside of the high intensity electric field regionassociated with the RF circuit waves. Paths established between therespective periodic circuit elements 28 and the conductive envelope 4,which acts as a heat sink, are still efiiciently maintained to providefor the rapid dissipation of the thermal energy generated by theinteraction process.

Referring next to FIG. 3, as well as FIG. 4, which is rotated 90 fromthe plane of FIG. 3, the attenuation means for the suppression ofundesired oscillation is provided by the vanetype attenuator members 34.In this embodiment each attenuator member has a slight inner taperededge 36. Attenuator members 34 are arranged in oppositely disposed pairsin the backwall region oriented 90 from the positioning of supportmembers 30. A strip or vane of a dielectric material similar to thesupport member material is coated with a lossy or resistive materialsuch as graphite or carbon. The attenuation means is thus provided overa selected region spanning a number of periodic circuit elements. Theattenuator members may be thinner than the support members and have aminimal effect on dielectric or backwall loading to disrupt the delayline electrical characteristics. The attenuator members, if desired, cancontact the circuit elements 28 and are easily adjusted axially, as wellas radially, to vary the quantity of attenuating material. Any resistivematerials may also be employed for the attenuation means.

FIG. 5 illustrates another feature of the invention relating to theseparate support and attenuator members. In the selected regionsadjacent to the helix delay line structure, additional attenuation isprovided by additional attenuator members 38 angularly displaced asillustrated. In addition, further attenuation may be provided by similarmembers 40. The provision of the attenuating material as an independentcomponent results in an attenuator which is superior to the surfacecoatings applied to the insulator support members in prior art delayline structures.

Referring next to FIG. 6, another feature of the invention isillustrated. A pair of oppositely disposed attenuator members 42supported by the envelope 4 are disposed in the backwall region of thehelix delay line structure 20. A tapered undulating edge 44 provides forthe disposition of a gradually reducing quantity of the attenuatingmaterial in the interstices between circuit elements 28. It is,therefore, possible to provide for the introduction of the attenuationmeans in the regions of high electric fields over a shorter span of theoverall delay line length. A smaller attenuator would be required sothat a shorter tube length or higher output powers may be realized.

Many other variations, modifications or alterations will occur to thoseskilled in the art. Numerous other materials for the support andattenuation functions may also be utilized.

The independent provision of the support and attenuation means optimizesthe output power capability of the traveling wave device with thereduction of "dielectric loading" bridging the delay line elements. Thedisclosed new and novel structure also provides conformation to the RFelectric field intensity pattern with higher efiiciency in the electronbeamcircuit wave coupling. It is intended, therefore, that the foregoingdescription of preferred embodiments be considered in the broadestaspects and not in a limiting sense.

What is claimed is:

1. A traveling wave device comprising:

an envelope;

means for propagating electromagnetic wave energy along a predeterminedpath; and

dielectric means for supporting said wave propagating means contactingsaid envelope;

said dielectric means having an undulating wall configuration contactingsaid wave propagating means with said Wall conforming substantially tothe intensity pattern of the electric fields associated with thepropagated electromagnetic waves with the lesser amount of dielectricmaterial being disposed in the regions of high electric field intensity.

2. A traveling wave device comprising:

an envelope;

means for propagating electromagnetic wave energy along a predeterminedpath;

dielectric means for supporting said wave propagating means contactingsaid envelope;

said dielectric means having an undulating wall configuration contactingsaid wave propagating means with said wall conforming substantially tothe intensity pattern of the electric fields associated with thepropagated electromagnetic waves with the lesser amount of dielectricmaterial being disposed in the regions of high electric field intensity;and

lossy energy absorbing means for attenuating said wave energy appendedto said envelope in the spaces between said dielectric means.

3. A traveling wave device comprising:

an envelope;

a plurality of spaced periodic circuit elements forming anelectromagnetic wave energy propagating structure; dielectric means forsupporting said circuit elements contacting an inner wall of saidenvelope;

said dielectric means contacting each of said circuit elements andhaving arch-shaped notches in the intervals between said circuitelements; and

lossy energy absorbing means for attenuating said wave energy appendedto said envelope in the spaces between said dielectric means.

4. A device according to claim 3 wherein said attenuating means comprisevane members defining wall structure providing a larger amount ofattenuating material in the intervals between said circuit elements overa portion of the vane member axial length.

1. A traveling wave device comprising: an envelope; means forpropagating electromagnetic wave energy along a predetermined path; anddielectric means for supporting said wave propagating means contactingsaid envelope; said dielectric means having an undulating wallconfiguration contacting said wave propagating means with said wallconforming substantially to the intensity pattern of the electric fieldsassociated with the propagated electromagnetic waves with the lesseramount of dielectric material being disposed in the regions of highelectric field intensity.
 2. A traveling wave device comprising: anenvelope; means for propagating electromagnetic wave energy along apredetermined path; dielectric means for supporting said wavepropagating means contacting said envelope; said dielectric means havingan undulating wall configuration contacting said wave propagating meanswith said wall conforming substantially to the intensity pattern of theelectric fields associated with the propagated electromagnetic waveswith the lesser amount of dielectric material being disposed in theregions of high electric field intensity; and lossy energy absorbingmeans for attenuating said wave energy appended to said envelope in thespaces between said dielectric means.
 3. A traveling wave devicecomprising: an envelope; a plurality of spaced periodic circuit elementsforming an electromagnetic wave energy propagating structure; dielectricmeans for supporting said circuit elements contacting an inner wall ofsaid envelope; said dielectric means contacting each of said circuitelements and having arch-shaped notches in the intervals between saidcircuit elements; and lossy energy absorbing means for attenuating saidwave energy appended to said envelope in the spaces between saiddielectric means.
 4. A device according to claim 3 wherein saidaTtenuating means comprise vane members defining wall structureproviding a larger amount of attenuating material in the intervalsbetween said circuit elements over a portion of the vane member axiallength.